Intershaft seal system for minimizing pressure induced twist

ABSTRACT

An intershaft seal system capable of communicating a balanced pressure profile onto forward and aft faces along a piston ring is presented. The seal system includes forward and aft mating rings and a piston ring. Mating rings include a plurality of divergent flow grooves adjacent to the piston ring. Each divergent flow groove includes a pair of grooves which intersect at and are substantially symmetric about an apex. The piston ring includes channels which direct a fluid from a high pressure region upward or downward and through the piston ring and onto the divergent flow grooves. The divergent flow grooves separate the fluid in a symmetrically divergent fashion prior to communication onto the piston ring. The divergent flow grooves communicate a substantially symmetric pressure force onto each side of the piston ring so as to minimize twist thereof, thus reducing wear along the piston ring and increasing seal life.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S.Non-Provisional application Ser. No. 13/504,302 filed Apr. 26, 2012which is a national phase application based upon Patent CooperationTreaty Application No. PCT/US2010/049030 filed Sep. 16, 2010, bothentitled Intershaft Seal System for Minimizing Pressure Induced Twist,which are hereby incorporated in their entirety by reference thereto.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a seal for use within an intershaftassembly. Specifically, the invention is a sealing system includingdivergent flow grooves which separate fluid, originating from a highpressure region, communicated onto each apex along the divergent flowgrooves so as to produce a balanced pressure profile radially widthwiseacross a piston ring disposed between concentric, rotatable inner andouter shafts. The divergent flow grooves minimize twist along a pistonring otherwise produced by conventional hydrodynamic grooves along amating ring. The invention is applicable to a variety of uses whereinconcentric shafts are disposed in a co-rotating or counter-rotatingarrangement, one specific non-limiting example being a turbine engine.

2. Background

Intershaft seal systems and hydrodynamic grooves are both known withinthe seal art.

Lipschitz describes a circumferential inter-seal for sealing betweenrelatively rotatable concentric shafts in U.S. Pat. No. 4,972,986. Withreference to FIG. 1, the intershaft seal assembly 1 includes a forwardmating ring 4 adjacent to a high pressure region and an aft mating ring5 adjacent to a low pressure region. Mating rings 4, 5 are disposedabout a seal ring 6. A spacer ring 8 is concentrically aligned with theseal ring 6 and separated therefrom via an annular space 10. The spacerring 8 is wider than the seal ring 6 so as to contact both forward andaft mating rings 4, 5, thus allowing the seal ring 6 to translatebetween the mating rings 4, 5. The mating rings 4, 5, spacer ring 8, andseal ring 6 are disposed between an inner shaft 3 and an outer shaft 2which are concentric and rotatable in either a co-rotating orcounter-rotating fashion. The mating rings 4, 5 and spacer ring 8 aresecured to the inner shaft 3 via a stop ring 7 so as to rotate with theinner shaft 3. The seal ring 6 is dimensioned so as to at most partiallycontact the outer shaft 2 when the outer and inner shafts 2, 3 are atrest. The seal ring 6 further includes at least one circumferentialspace or gap which allows the seal ring 6 to flex or expand as itrotates so as to then contact and rotate with the outer shaft 2 separatefrom the inner shaft 3. Contact between the rotating seal ring 6 andmating rings 4, 5 is avoided to minimize friction-induced wear along thesides of the seal ring 6.

Contact between a rotating seal ring 6 and mating rings 4, 5 isminimized by a thin film interposed between the seal ring 6 and forwardmating ring 4 and between the seal ring 6 and aft mating ring 5. Thethin film is produced by communicating fluid, examples including but notlimited to air and air/oil mixture, from the high pressure region to thelow pressure region along a path defined by spaces between the seal ring6 and the outer and inner shafts 2, 3 and mating rings 4, 5, and axiallythrough passages.

With reference to FIGS. 1-3, fluid flows from the higher pressure regionthrough a plurality of horizontal ports 9 through the forward matingring 4 and across a forward annular space 12 between the forward matingring 4 and outer shaft 2. The same fluid flows around the seal ring 6and through the seal ring 6 via horizontal ports 14. Thereafter, thefluid flows to the lower pressure region via an aft annular space 13between the outer shaft 2 and the aft mating ring 5.

The forward and aft mating rings 4, 5 include a plurality of spiralgrooves 11, as shown in FIGS. 2 and 3. The spiral grooves 11 include aplurality of recessed arcuate slots along the surface of the forward andaft mating rings 4, 5. The spiral grooves 11 communicate a hydrodynamiclift force onto the seal ring 6 via a pressure field along the spacesbetween the mating rings 4, 5 and seal ring 6. This hydrodynamic liftforce increases exponentially as the seal ring 6 translates toward oneof the mating rings 4, 5, thereby preventing the seal ring 6 fromcontacting the mating rings 4, 5 under dynamic conditions. FIGS. 4 and 5graphically present non-symmetric pressure profiles produced by theforward and aft mating rings 4, 5, respectively, across the width of theseal ring 6.

It is well known that large non-symmetric counter forces generated byhydrodynamic grooves cause a sealing ring to twist thus compromising theparallelism between the mating rings or runners and the sealing ring.Often, the result is radial and angular distortions which produce“coning” along the sealing ring. Coning is understood to cause excessivewear along a sealing ring and to degrade the performance of a sealingsystem.

Lipschitz explicitly recognizes this problem and suggests for thesealing ring to be composed of materials having a high modulus ofelasticity to minimize undesirable radial and angular deflectionsimposed by unbalanced hydrodynamic forces. As such, Lipschitz teachesaway from pressure-based solutions to the twisting problem.

With reference to FIGS. 6 and 7 a-7 c, another intershaft seal assembly30 is shown including a forward mating ring 33 and an aft mating ring 34disposed about a piston ring 35 between rotatable inner and outer shafts31, 32. The piston ring 35 is concentrically aligned with a spacer ring36, so that the piston ring 35 translates between the forward and aftmating rings 33, 34. The piston 35 and spacer ring 36 are separated byan annular gap 40. The piston ring 35 is dimensioned and includes one ormore gaps so as to flex or expand as the inner and outer shafts 31, 32rotate, thereby contacting the outer shaft 32 and rotating therewith.The forward and aft mating rings 33, 34 and spacer ring 36 are securedto a carrier 37 via a stop ring 54 so as to rotate with the inner shaft31. An annular space 38, 39 is provided along the forward mating ring 33and aft mating ring 34, respectively, so as to avoid contact with theouter shaft 32. Fluid from the high pressure region passes over theforward mating ring 33, around the piston ring 35, and then over the aftmating ring 34 into the low pressure region.

In this design, conventional hydrodynamic grooves are positioned alongthe faces 42, 41 of the forward and aft mating rings 33, 34,respectively, to improve flow around the piston ring 35 and to minimizecontact between the piston ring 35 and mating rings 33, 34. The face 41along the aft mating ring 34 includes a plurality of outward flowhydrodynamic grooves 43, as represented in FIG. 7 b. The face 42 of theforward mating ring 33 includes a plurality of inward flow hydrodynamicgrooves 44, as represented in FIG. 7 c. Hydrodynamic grooves 43, 44 aregenerally arcuate-shaped, shallow slots along the surface of therespective mating rings 33, 34.

With reference to FIG. 7 d, the inward and outward flow hydrodynamicgrooves 44, 43 each communicate a generally non-symmetric,triangular-shaped pressure profile 15, 16 onto opposing sides of thepiston ring 35. This means that the piston ring 35 experiences higherpressures and larger unbalanced forces near the inner diameter along theforward mating ring 33 and near the outer diameter along the aft matingring 34. The resultant deflections cause the piston ring 35 to twist 17allowing the piston ring 35 to rub against the aft mating ring 34 so asto impart a wear pattern 18 with pronounced wear depth 45 adjacent tothe inner diameter of the piston ring 35. Similar wear is likewisepossible along the piston ring 35 near the outer diameter adjacent tothe forward mating ring 33. In this example, material properties aloneare not sufficient to avoid the distortions and wear at the higherrelative rotational speeds required to further improve the performanceof turbine engines with concentrically rotating shafts.

Lindeboom describes a straight leakoff seal for use within a centrifugalpump in U.S. Pat. No. 3,751,045. With reference to FIGS. 8 and 9, thecentrifugal pump 20 includes a housing 21 with a collar 23 disposedabout a drive shaft 22. An annular dam 26 is disposed along a sealingring 24 toward the outer diameter thereof adjacent to the high-pressureend of the centrifugal pump 20. A plurality of v-shaped grooves 25 areequally spaced circumferentially about sealing ring 24. The v-shapedgrooves 25 pump fluid from an outer region to an inner region byallowing the fluid to enter one end and exit the other end of thev-shaped grooves 25 causing the face pressure profile to grow, thuspreventing contact between the sealing ring 24 and collar 23. As such,Lindeboom does not allow for apex-centric flow patterns along thev-shaped grooves 25.

Lindeboom describes the advantages of his invention via reference to thepressure profiles reproduced in FIG. 10, wherein reference “B” describesthe non-hydrodynamic pressure forces acting along the back end of thesealing ring 24, reference “C” describes the hydrodynamic pressureforces acting along the interface between the collar 23 and sealing ring24, and reference “D” describes the maximum restoring forces whichprevent contact between the sealing ring 24 and collar 23 under dynamicrunning conditions. The pressure profiles reported by Lindeboom alongthe interface across the dam 26 and between the collar 23 and sealingring 24 across the sealing ring 24 are non-symmetric. As such, Lindeboomneither suggests nor teaches the generation of a symmetric pressureprofile along the width of a seal ring via symmetrically-shaped grooves.

As is readily apparent from the discussions above, the related arts donot include an intershaft seal system which minimizes twist along a sealor piston ring via the communication of a substantially symmetricpressure field across the width of the ring via a plurality ofsubstantially symmetric hydrodynamic pockets.

Accordingly, what is required is an intershaft seal system whichcommunicates a substantially symmetric pressure field across the widthof a piston ring onto both sides thereof via a plurality ofsubstantially symmetric hydrodynamic pockets which receive fluid from ahigh pressure region and separate the flow in a divergent fashion priorto communicating the fluid onto the ring.

SUMMARY OF THE INVENTION

An object of the invention is to provide an intershaft seal system whichcommunicates a substantially symmetric pressure field across the widthof a piston ring onto both sides thereof via a plurality ofsubstantially symmetric hydrodynamic pockets which receive fluid from ahigh pressure region and separate the flow in a divergent fashion priorto communicating the fluid onto the ring.

In accordance with some embodiments, the intershaft seal system includesa forward mating ring adjacent to a high pressure region and an aftmating ring adjacent to a low pressure region whereby both rings aredisposed between an outer shaft and an inner shaft which are concentricand separately rotatable. The forward and aft mating rings areseparately disposed about and separately rotatable from a piston ring.The forward and aft mating rings each have a plurality of divergent flowgrooves thereon. Each divergent flow groove includes a pair of grooveswhich intersect at an apex. The piston ring includes a plurality ofsubstantially vertical channels. Each substantially vertical channeldirectly communicates at one end with an outer diameter surface anddirectly communicates at another end with a substantially horizontalchannel. Each substantially horizontal channel is communicable with oneapex along the forward mating ring and one apex along the aft matingring. The outer diameter surface includes at least one outer groovedirectly contacting a dam. A fluid from the high pressure region isdirected through each substantially vertical channel into thesubstantially horizontal channel and then onto the apexes as the pistonring rotates with respect to the divergent flow grooves. Each apexdirects the fluid into the pair of grooves. The divergent flow groovesproduce a substantially symmetric fluid pressure along a forward faceand an aft face of the piston ring so as to minimize twist along thepiston ring.

In accordance with other embodiments, the substantially verticalchannels extend from the outer diameter surface inward toward the innershaft.

In accordance with other embodiments, a depth varies along at least onedivergent flow groove.

In accordance with other embodiments, a width varies along at least onedivergent flow groove.

In accordance with other embodiments, each end of the substantiallyhorizontal channel directly communicates with a groove whereby onegroove is disposed along the aft face and another groove is disposedalong the forward face. Each groove is communicable with at least oneapex.

In accordance with other embodiments, the aft mating ring includes aplurality of holes which allow the fluid to enter the low pressureregion.

In accordance with other embodiments, the dam prevents flow of the fluidbetween the piston ring and the outer shaft.

In accordance with other embodiments, the outer groove directlycommunicates with the substantially vertical channel.

In accordance with some embodiments, the intershaft seal system includesa forward mating ring adjacent to a high pressure region and an aftmating ring adjacent to a low pressure region whereby both rings aredisposed between an outer shaft and an inner shaft which are concentricand separately rotatable. The forward and aft mating rings each have aplurality of divergent flow grooves thereon. Each divergent flow grooveincludes a pair of grooves which intersect at an apex. The piston ringincludes a plurality of substantially vertical channels. Eachsubstantially vertical channel directly communicates at one end with aninner diameter surface along the piston ring and directly communicatesat another end with a substantially horizontal channel. Eachsubstantially horizontal channel is communicable with one apex along theforward mating ring and one apex along the aft mating ring. The forwardmating ring includes at least one port which communicates a fluid to theinner diameter surface. The fluid from the high pressure region isdirected through each substantially vertical channel into thesubstantially horizontal channel and then onto the apexes as the pistonring rotates with respect to the divergent flow grooves. The apexdirects the fluid into the pair of grooves. The divergent flow groovesproduce a substantially symmetric fluid pressure along a forward faceand an aft face of the piston ring so as to minimize twist along thepiston ring.

In accordance with other embodiments, the substantially verticalchannels extend from the inner diameter surface outward toward the outershaft.

In accordance with other embodiments, a depth varies along at least onedivergent flow groove.

In accordance with other embodiments, a width varies along at least onedivergent flow groove.

In accordance with other embodiments, each end of the substantiallyhorizontal channel directly communicates with a groove whereby onegroove is disposed along the aft face and one groove is disposed alongthe forward face. Each groove is communicable with at least one apex.

In accordance with other embodiments, the outer diameter surfaceincludes at least one outer groove directly contacting a dam. The damprevents flow of the fluid between the piston ring and the outer shaft.

In accordance with some embodiments, a method is provided for minimizingtwist along a piston disposed between an inner shaft and an outer shaft.Fluid is communicated from a high pressure region to a low pressureregion separated by the piston ring disposed between a forward matingring and an aft mating ring. The piston ring includes a plurality ofsubstantially vertical channels. Each substantially vertical channeldirectly communicates at one end with an outer diameter surface anddirectly communicates at another end with a substantially horizontalchannel. Each substantially horizontal channel also communicates withone apex along the forward mating ring and one the apex along the aftmating ring. The fluid is directed onto a plurality of divergent flowgrooves disposed along the forward mating ring and the aft mating ring.Each divergent flow groove includes a pair of grooves which intersect atan apex. The fluid enters each substantially vertical channel and passesinto the substantially horizontal channel exiting onto the apexes as thepiston ring rotates with respect to the divergent flow grooves. The pairof grooves is substantially symmetric about the apex. The fluid impingesthe apexes so that the fluid flows into the pairs of grooves. A firstfluid pressure force is produced along the forward face of the pistonring via the divergent flow grooves. The first fluid pressure force issubstantially symmetric across a radial width of the piston ring. Asecond fluid pressure force is produced along the aft face of the pistonring via the divergent flow grooves. The second fluid pressure force issubstantially symmetric across the radial width of the piston ring. Thefirst and second fluid pressure forces are substantially balanced.

In accordance with other embodiments, the fluid enters the substantiallyvertical channel adjacent to the outer diameter surface.

In accordance with other embodiments, the fluid enters the low pressureregion via a plurality of holes along the aft mating ring.

In accordance with other embodiments, the forward and aft faces eachinclude at least one arcuate groove communicable with at least onehorizontal channel so that each arcuate groove is communicable with atleast one apex.

In accordance with some embodiments, a method is provided for minimizingtwist along a piston disposed between an inner shaft and an outer shaft.Fluid is communicated from a high pressure region to a low pressureregion separated by the piston ring disposed between a forward matingring and an aft mating ring. The piston ring includes a plurality ofsubstantially vertical channels. Each substantially vertical channeldirectly communicates at one end with an inner diameter surface alongthe piston ring and directly communicates at another end with asubstantially horizontal channel. Each substantially horizontal channelalso communicates with one apex along the forward mating ring and oneapex along the aft mating ring. The forward mating ring includes atleast one port which communicates a fluid to the inner diameter surface.The fluid is directed onto a plurality of divergent flow groovesdisposed along the forward mating ring and the aft mating ring. Eachdivergent flow groove includes a pair of grooves which intersect at anapex. The fluid enters each substantially vertical channel and passesinto the substantially horizontal channel exiting onto the apexes as thepiston ring rotates with respect to the divergent flow grooves. The pairof grooves is substantially symmetric about the apex. The fluid impingesthe apexes so that the fluid flows into the pairs of grooves. A firstfluid pressure force is produced along the forward face of the pistonring via the divergent flow grooves. The first fluid pressure force issubstantially symmetric across a radial width of the piston ring. Asecond fluid pressure force is produced along the aft face of the pistonring via the divergent flow grooves. The second fluid pressure force issubstantially symmetric across the radial width of the piston ring. Thefirst and second fluid pressure forces are substantially balanced.

In accordance with other embodiments, the fluid enters the substantiallyvertical channel adjacent to the inner diameter surface.

In accordance with other embodiments, the fluid is communicated to theinner diameter surface via at least one port.

In accordance with other embodiments, the forward and aft faces eachinclude at least one arcuate groove communicable with at least onehorizontal channel so that each arcuate groove is communicable with atleast one apex.

Several advantages are offered by the invention. The invention minimizesdistortional effects along a piston ring caused by hydrodynamic loadswhich otherwise prevent the ring from contacting a mating ring as thepiston ring translates between a pair of mating rings. The inventionexploits the symmetry of the divergent flow grooves so as to produce asubstantially symmetric pressure field communicable radially widthwiseacross a piston ring. The invention minimizes piston ring wear withinturbine engines including counter-rotating shafts operating at highrotational speeds, thus reducing engine maintenance.

BRIEF DESCRIPTION OF THE INVENTION

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view illustrating an intershaft sealassembly disposed between rotatable, concentric inner and outer shaftsand further including a seal ring disposed between a pair of matingrings as described by Lipschitz in U.S. Pat. No. 4,972,986.

FIG. 2 is a cross-sectional view from FIG. 1 illustrating the innersurface of the forward mating ring with a plurality of spiral groovesdisposed thereon.

FIG. 3 is a cross-sectional view from FIG. 1 illustrating the innersurface of the aft mating ring with a plurality of spiral groovesdisposed thereon.

FIG. 4 is a schematic illustrating the distribution of fluid pressuresalong the forward surface of the seal ring in FIG. 1.

FIG. 5 is a schematic illustrating the distribution of fluid pressuresalong the aft surface of the seal ring in FIG. 1.

FIG. 6 is a partial cross-sectional view illustrating another intershaftseal assembly disposed between counter-rotating inner and outer shaftsand further including forward and aft mating rings disposed along acarrier about a piston ring.

FIG. 7 a is a cross-sectional view illustrating the intershaft sealassembly in FIG. 6.

FIG. 7 b is a front side view illustrating a plurality of outward flowhydrodynamic grooves disposed along the face of the aft mating ring inFIG. 7 a.

FIG. 7 c is a front side view illustrating a plurality of inward flowhydrodynamic grooves disposed along the face of the forward mating ringin FIG. 7 a.

FIG. 7 d is an enlarged exploded cross-sectional view illustrating thewear pattern along the piston ring in FIG. 7 a caused by the fluidpressure forces induced by the inward and outward grooves along themating rings onto the piston ring.

FIG. 8 is a partial section view illustrating a seal assembly within acentrifugal pump as described by Lindeboom in U.S. Pat. No. 3,751,045.

FIG. 9 is an enlarged fragmentary view illustrating a plurality ofv-shaped grooves disposed along the face of the seal ring in FIG. 8.

FIG. 10 is a schematic illustrating the distribution of fluid pressureforces along the collar in FIG. 8.

FIG. 11 a is a cross-sectional view illustrating an intershaft sealsystem including a piston ring with channels that direct fluid from thehigh pressure region upward and onto a plurality of divergent flowgrooves disposed along the aft mating ring so as to produce asubstantially symmetric fluid pressure profile across the width of theaft face of the piston ring in accordance with an embodiment of theinvention.

FIG. 11 b is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the aft mating ring in accordancewith an embodiment of the invention.

FIG. 11 c is an enlarged side view illustrating outward flowhydrodynamic grooves disposed along the face of the forward mating ringin accordance with an embodiment of the invention.

FIG. 11 d is an enlarged side view illustrating substantially symmetricdivergent flow grooves oriented along the aft mating ring whereby flowentering substantially near the apex of each divergent flow groove isseparated into the groove pair in accordance with an embodiment of theinvention.

FIG. 11 e is an enlarged section view illustrating channels disposedwithin the piston ring which direct fluid originating from the highpressure region upward onto the face of the aft mating ring adjacent tothe apex of each divergent flow groove in accordance with an embodimentof the invention.

FIG. 11 f is an enlarged side view illustrating the outlets along theaft face of the piston ring with optional grooves that simultaneouslycommunicate fluid onto the apex of one or more divergent flow groovesalong the face of the mating ring in accordance with an embodiment ofthe invention.

FIG. 11 g is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across and around theforward mating ring, piston ring, and aft mating ring in accordance withan embodiment of the invention.

FIG. 11 h is a schematic illustrating steady-state fluid pressures aboutthe cross section of a piston ring with particular reference to thesubstantially symmetric pressure profile along the aft face about theapexes of the divergent flow grooves in accordance with an embodiment ofthe invention.

FIG. 11 i is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across and around theforward mating ring, piston ring with dam adjacent to the high pressureregion, and aft mating ring in accordance with an embodiment of theinvention.

FIG. 11 j is a schematic illustrating steady-state fluid pressures aboutthe cross section of a piston ring having a dam adjacent to the highpressure region with particular reference to the substantially symmetricpressure profile along the aft face about the apexes of the divergentflow grooves and reduced pressure profile along the outer diameter ofthe piston ring in accordance with an embodiment of the invention.

FIG. 12 a is an enlarged cross-sectional view illustrating an intershaftseal system including a forward mating ring and a piston ring withchannels that direct fluid from the high pressure region onto the apexesof a plurality of divergent flow grooves disposed along the forward andaft mating rings so as to produce substantially symmetric fluid pressureforces across the width of the forward and aft faces of the piston ringin accordance with an embodiment of the invention.

FIG. 12 b is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the aft mating ring in accordancewith an embodiment of the invention.

FIG. 12 c is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the forward mating ring in accordancewith an embodiment of the invention.

FIG. 12 d is an enlarged side view illustrating the divergent flowgrooves which are each substantially symmetric about an apex andoriented along the forward mating ring so as to separate the flowentering each groove substantially near the apex via a port inaccordance with an embodiment of the invention.

FIG. 12 e is an enlarged section view illustrating channels disposedwithin the piston ring which direct fluid originating from the highpressure region downward onto the face of the aft mating ring adjacentto the apex of each divergent flow groove in accordance with anembodiment of the invention.

FIG. 12 f is an enlarged side view illustrating the outlets along theaft face of the piston ring with optional upper grooves which directfluid into the channels within the piston ring and optional grooves thatsimultaneously communicate fluid onto one or more apexes of thedivergent flow grooves along the face of the mating ring in accordancewith an embodiment of the invention.

FIG. 12 g is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across the forwardmating ring, piston ring, and aft mating ring in accordance with anembodiment of the invention.

FIG. 12 h is a schematic illustrating steady-state fluid pressure forcesabout the cross section of a piston ring with particular reference tothe substantially symmetric pressure profiles along the forward and aftfaces adjacent to the divergent flow grooves in accordance with anembodiment of the invention.

FIG. 12 i is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across the forwardmating ring, piston ring with dam adjacent to the high pressure region,and aft mating ring in accordance with an embodiment of the invention.

FIG. 12 j is a schematic illustrating steady-state fluid pressure forcesabout the cross section of a piston ring having a dam adjacent to thehigh pressure region with particular reference to the substantiallysymmetric pressure profiles along the forward and aft faces adjacent tothe divergent flow grooves and reduced pressure along the outer diameterof the piston ring in accordance with an embodiment of the invention.

FIG. 13 a is an enlarged cross-sectional view illustrating an intershaftseal system including a piston ring with channels that direct fluid fromthe high pressure region downward onto a plurality of divergent flowgrooves disposed along the aft mating ring so as to producesubstantially symmetric fluid pressure forces across the width of theaft face of the piston ring in accordance with an embodiment of theinvention.

FIG. 13 b is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the aft mating ring in accordancewith an embodiment of the invention.

FIG. 13 c is an enlarged side view illustrating outward flowhydrodynamic grooves disposed along the face of the forward mating ringin accordance with an embodiment of the invention.

FIG. 13 d is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across the forwardmating ring, piston ring, and aft mating ring in accordance with anembodiment of the invention.

FIG. 13 e is a schematic illustrating steady-state fluid pressures aboutthe cross section of a piston ring with particular reference to thesubstantially symmetric pressure profile along the aft face adjacent tothe divergent flow grooves in accordance with an embodiment of theinvention.

FIG. 14 a is a plan view illustrating a divergent flow groove includingtwo grooves intersecting at an apex whereby the groove width decreaseswith distance from the apex in accordance with an embodiment of theinvention.

FIG. 14 b is a cross-sectional view illustrating a divergent flow groovewhereby the groove depth decreases with distance from the apex inaccordance with an embodiment of the invention.

FIG. 15 a is a plan view illustrating a hydrodynamic groove whereby thegroove width decreases opposite of the rotational direction inaccordance with an embodiment of the invention.

FIG. 15 b is a cross-sectional view illustrating a groove whereby thegroove depth decreases opposite of the rotational direction inaccordance with an embodiment of the invention.

FIG. 16 a is an enlarged cross-sectional view illustrating an intershaftseal system including a piston ring with channels that direct fluid fromthe high pressure region onto the apexes of a plurality of divergentflow grooves disposed along the forward and aft mating rings so as toproduce substantially symmetric fluid pressure forces across the widthof the forward and aft faces of the piston ring in accordance with anembodiment of the invention.

FIG. 16 b is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the aft mating ring in accordancewith an embodiment of the invention.

FIG. 16 c is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the forward mating ring in accordancewith an embodiment of the invention.

FIG. 16 d is an enlarged section view illustrating channels disposedwithin the piston ring which direct fluid originating from the highpressure region downward onto the face of the forward and aft matingrings adjacent to the apex of each divergent flow groove in accordancewith an embodiment of the invention.

FIG. 16 e is an enlarged side view illustrating the outlets along theaft face of the piston ring with optional upper grooves which directfluid into the channels within the piston ring and optional grooves thatsimultaneously communicate fluid onto one or more apexes of thedivergent flow grooves along the face of the mating ring in accordancewith an embodiment of the invention.

FIG. 16 f is an enlarged side view illustrating the outlets along theforward face of the piston ring with optional upper grooves which directfluid into the channels within the piston ring and optional grooves thatsimultaneously communicate fluid onto one or more apexes of thedivergent flow grooves along the face of the mating ring in accordancewith an embodiment of the invention.

FIG. 16 g is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across the forwardmating ring, piston ring, and aft mating ring in accordance with anembodiment of the invention.

FIG. 16 h is a schematic illustrating steady-state fluid pressure forcesabout the cross section of a piston ring with particular reference tothe substantially symmetric pressure profiles along the forward and aftfaces adjacent to the divergent flow grooves in accordance with anembodiment of the invention.

FIG. 17 a is a cross-sectional view illustrating an intershaft sealsystem including a piston ring with channels that direct fluid from thehigh pressure region upward and onto a plurality of divergent flowgrooves disposed along the forward and aft mating rings so as to producea substantially symmetric fluid pressure profile across the width of theforward and aft faces of the piston ring in accordance with anembodiment of the invention.

FIG. 17 b is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the aft mating ring in accordancewith an embodiment of the invention.

FIG. 17 c is an enlarged side view illustrating the divergent flowgrooves disposed along the face of the forward mating ring in accordancewith an embodiment of the invention.

FIG. 17 d is an enlarged section view illustrating channels disposedwithin the piston ring which direct fluid originating from the highpressure region upward onto the face of the forward and aft mating ringsadjacent to the apex of each divergent flow groove in accordance with anembodiment of the invention.

FIG. 17 e is an enlarged side view illustrating the outlets along theforward face of the piston ring with optional grooves thatsimultaneously communicate fluid onto the apex of one or more divergentflow grooves along the face of the mating ring in accordance with anembodiment of the invention.

FIG. 17 f is an enlarged side view illustrating the outlets along theaft face of the piston ring with optional grooves that simultaneouslycommunicate fluid onto the apex of one or more divergent flow groovesalong the face of the mating ring in accordance with an embodiment ofthe invention.

FIG. 17 g is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across and around theforward mating ring, piston ring, and aft mating ring in accordance withan embodiment of the invention.

FIG. 17 h is a schematic illustrating steady-state fluid pressures aboutthe cross section of a piston ring with particular reference to thesubstantially symmetric pressure profile along the forward and aft facesabout the apexes of the divergent flow grooves in accordance with anembodiment of the invention.

FIG. 17 i is an enlarged exploded cross-sectional view illustrating flowpatterns between the high and low pressure regions across and around theforward mating ring, piston ring with dam adjacent to the high pressureregion, and aft mating ring in accordance with an embodiment of theinvention.

FIG. 17 j is a schematic illustrating steady-state fluid pressures aboutthe cross section of a piston ring having a dam adjacent to the highpressure region with particular reference to the substantially symmetricpressure profile along the forward and aft faces about the apexes of thedivergent flow grooves and reduced pressure profile along the outerdiameter of the piston ring in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to several preferred embodiments ofthe invention that are illustrated in the accompanying drawings.Wherever possible, same or similar reference numerals are used in thedrawings and the description to refer to the same or like parts orsteps. The drawings are in simplified form and are not to precise scale.

While features of various embodiments are separately describedthroughout this document, it is understood that two or more suchfeatures could be combined into a single embodiment.

While the invention is described with particular reference to theintershaft seal assembly 30 shown in FIG. 6, it is understood that theinvention is likewise applicable to other intershaft assemblies whereina seal is provided between concentrically aligned and rotating inner andouter shafts 31, 32, including but not limited to the assembly describedby Lipschitz in U.S. Pat. No. 4,972,986. The inner and outer shafts 31,32 are not shown for the drawings discussed below.

Piston ring 35, forward and aft mating rings 33, 34, spacer ring 36,stop ring 54, and carrier 37 are composed of materials understood in theart.

The divergent flow grooves 47 described herein are manufactured viamethods understood in the art.

Pressure diagrams are representative of gauge pressures. The symmetricpressure profiles described herein are exemplary of the cross-sectionalshapes which could be communicated onto a piston ring 35. However, othersymmetric cross sectional profiles are possible.

Referring now to FIGS. 11 a-11 c, the seal system 29 is shown includinga piston ring 35 interposed between a forward mating ring 33 and an aftmating ring 34. A spacer ring 36 is arranged concentrically with thepiston ring 35. The spacer ring 36 is wider than the piston ring 35 soas to contact the forward and aft mating rings 33, 34, thereby allowingthe piston ring 35 to translate between the mating rings 33, 34. Theforward and aft mating rings 33, 34 and spacer ring 36 contact a carrier37 about an inner shaft 31, shown in FIG. 6, and are secured thereto viaa stop ring 54 so as to be rotatable with the inner shaft 31. Theforward and aft mating rings 33, 34 include grooves disposed along asurface immediately adjacent to the piston ring 35.

The piston ring 35 is dimensioned to have an inner diameter larger thanthe outer diameter of the spacer ring 36 so as to form an annular gap 40therebetween. The piston ring 35 is also preferred to have an outerdiameter which either avoids or limits contact with the inner diameterof the outer shaft 32 when the outer shaft 32 is at rest. The pistonring 35 also includes one or more design features known within the art,one example being the gap 56 shown in FIGS. 11 f and 12 f, which allowthe piston ring 35 to flex or expand diametrically so as to contact theouter shaft 32 as the piston ring 35 and outer shaft 32 rotate. Thecontact forces between the piston ring 35 and outer shaft 32 should besufficient so that the piston ring 35 moves with the outer shaft 32while avoiding and/or minimizing friction-induced wear therebetween.Also, contact between the piston ring 35 and outer shaft 32 is preferredto restrict fluid from flowing directly from the high pressure region tothe low pressure region.

A plurality of divergent flow grooves 47 could be provided along theface 41 of the aft mating ring 34 and another plurality of outward flowhydrodynamic grooves 43 could be provided along the face 42 of theforward mating ring 33. It is also understood that the forward face 42could include other types of hydrodynamic grooves known within the art,including but not limited to inward flow grooves.

The divergent flow grooves 47 and outward flow hydrodynamic grooves 43are located along the faces 41, 42, respectively, so as to overlay atleast a portion of the radial width (W_(P)) of the piston ring 35,preferably overlaying the piston ring 35 during transient andsteady-state operations of the turbine. This arrangement ensures thatthe grooves 43, 47 communicate a hydrodynamic force onto the piston ring35 regardless of its position between the mating rings 33, 34 and/orinner and outer shafts 31, 32.

As shown in FIG. 6, the forward and aft mating rings 33, 34 each have anouter diameter less than the inner diameter of the outer shaft 32. Theresultant spaces allow fluid to flow out of the high pressure region andinto the low pressure region. In some embodiments, a plurality of ports46 could be disposed through the forward mating ring 33 adjacent to thecarrier 37, however positioned so as to communicate fluid to the annulargap 40 between the piston ring 35 and spacer ring 36, as represented inFIGS. 11 a and 11 c. The ports 46 could be cylindrical-shaped holeswhich extend from the high pressure region through to the annular gap40. The ports 46 are disposed along the face 42 of the forward matingring 33 at one or more radial distances from the centerline of the innershaft 31. One or more ports 46 could be aligned immediately adjacent toeach outward flow hydrodynamic groove 43.

Referring now to FIG. 11 d, each divergent flow groove 47 could includea pair of grooves 27, 28 disposed along the face 41 of the aft matingring 34. The grooves 27, 28 are aligned in an intersecting fashion so asto form an apex 48. The grooves 27, 28 could include linear and/orarcuate-shaped shallow depressions or slots. The grooves 27, 28 arepreferred to be aligned symmetrically about the apex 48. The divergentflow grooves 47 are preferred to be aligned with the apexes 48 pointingtoward the direction of rotation so that fluid entering each apex 48 isdirected into the corresponding grooves 27, 28 resulting in the flowsgraphically represented in FIG. 11 d. The dimensions, shape, andalignment of the apex 48 and grooves 27, 28 should ensure that fluidentering the apex 48 is separated into two flows. The flows should be atleast substantially equal so as to communicate a substantially symmetricpressure profile about the axis of symmetry defined by the apex 48 andgrooves 27, 28.

In some embodiments, divergent flow grooves 47 could be aligned aboutthe aft mating ring 34 so that one or more apexes 48 are disposedbetween each pair of grooves 27, 28. For example, FIG. 11 d showsdivergent flow grooves 47 whereby one apex 48 from a neighboringdivergent flow groove 47 resides between each paired arrangement ofgrooves 27, 28. In other embodiments, the divergent flow grooves 47could be arranged end-to-end without overlap so that the apex 48 of eachdivergent flow groove 47 begins immediately or some distance from wherethe adjacent grooves 27, 28 end.

In order for the divergent flow grooves 47 to produce substantiallysymmetric pressures along at least a portion of the radial width (W_(P))of the piston ring 35, fluid is communicated onto each divergent flowgroove 47 so as to impinge at least a portion of the apex 48, thusallowing the resultant flow to be approximately equally divided betweenthe grooves 27, 28.

Referring now to FIGS. 11 e and 11 f, the piston ring 35 could include aplurality of channels 53 which direct fluid from the annular gap 40upward through the piston ring 35. In FIG. 11 e, the piston ring 35 isshown as an L-shaped channel 53 with a circular cross section whichforms a complete passage from the inner diameter surface 52 to the aftface 49 with outlet 62. However, other channel 53 designs are possible.The channels 53 are manufactured via methods understood in the art.

The channels 53 are separately disposed about the piston ring 35 in acircumferential fashion, as represented in FIG. 11 f, at a radius whichensures fluid exiting the channel 53 via the outlet 62 along the aftface 49 impinges the apexes 48 immediately adjacent thereto along theaft mating ring 34. In preferred embodiments, the centers of each outlet62 and each apex 48 should be at about the same radial distance from thecenterline of the inner shaft 31.

Referring again to FIG. 11 f, one or more generally arcuate-shapedgrooves 55 could be included along the aft face 49 of the piston ring35. Each groove 55 could be a pocket recessed along the piston ring 35about one or more outlets 62. The radial position of the grooves 55could overlay the apexes 48 along the aft mating ring 34. The length ofeach groove 55 could be sufficient so as to overlap one or more apexes48 as the piston ring 35 rotates with respect to the aft mating ring 34.This arrangement allows the fluid communicated through a channel 53 toexit the piston ring 35 into at least one groove 55 prior tocommunication onto one or more apexes 48 disposed along the aft matingring 34.

In some embodiments, a face dam could be provided along the forward faceof the piston ring 35. The face dam could include four or moreintersecting grooves that extend to the inner diameter of the pistonring 35. This feature would allow the low pressure, associated with thethrough holes along the aft mating ring 34, to extend up the forwardface of the piston ring 35 to reduce the axial closing force whichcauses the piston ring 35 to contact the aft mating ring 34. Theresultant pressure profile would break down over a smaller area ratherthan over the entire width of the piston ring 35.

Referring now to FIG. 11 g, an exemplary flow diagram is showndescribing one possible steady-state flow pattern between the high andlow pressure regions over the seal system 29 in FIG. 11 a. In thisembodiment, the fluid from the high pressure region passes over theforward mating ring 33 and through the forward mating ring 33 via theports 46. The fluid passing over the forward mating ring 33 is directeddownward, because of the contact between piston ring 35 and outer shaft32, along the space between the forward mating ring 33 and piston ring35 across the outward flow hydrodynamic grooves 43 so as to combine withthe fluid exiting the ports 46. Thereafter, the fluid passes through theannular gap 40 adjacent to the spacer ring 36 with a portion of thefluid entering the channels 53 and another portion passing upward alongthe space between the piston ring 35 and aft mating ring 34 across thedivergent flow grooves 47. The fluid passing through the channels 53exits the piston ring 35 via the outlet 62 impinging the divergent flowgrooves 47 as described herein. Thereafter, the fluid from the channels53 and annular gap 40 flows over the aft mating ring 34 into the lowpressure region.

Referring now to FIG. 11 h, an exemplary pressure diagram is showndescribing the steady-state pressures along the aft face 49, forwardface 50, outer diameter surface 51, and inner diameter surface 52 of thepiston ring 35 in FIG. 11 a.

The inner diameter pressure profile 60 is produced by the fluid withinthe annular gap 40 and is generally uniform along the inner diametersurface 52. The outer diameter pressure profile 59 could result from theoutward centrifugal forces acting along the piston ring 35 as it pressesagainst the outer shaft 32 and forces acting along the inner diametersurface 52. The outer diameter pressure profile 59 is generallynon-linear because of the flow pattern into the low pressure regionimmediately adjacent to the aft mating ring 34 near the outer diametersurface 51. The resultant force balance fixes the piston ring 35 to theouter shaft 32 so that both rotate together without sliding.

The forward pressure profile 58 results primarily from the hydrodynamicforces imposed along the piston ring 35 immediately adjacent to theforward face 50 via the outward flow hydrodynamic grooves 43. Thepressure profile is non-symmetric because pressure within a groovegenerally increases along the direction of flow.

The aft pressure profile 57 results primarily from the hydrodynamicforces imposed onto the aft face 49 of the piston ring 35 by thedivergent flow grooves 47. The aft pressure profile 57 is substantiallysymmetric about the apexes 48 of the divergent flow grooves 47.

Any asymmetries along the aft pressure profile 57 are due in part toasymmetries along the grooves 27, 28 about the apex 48 or ventingconditions along the aft face 49 adjacent to the outer and innerdiameter surfaces 51, 52. The pressure generally increases with distancefrom the apex 48 because orientation of the divergent flow grooves 47direct the flow pattern from the apex 48 towards the grooves 27, 28. Themaximum pressure could occur near the ends of grooves 27, 28, or one orboth ends of the piston ring 35, or near the outer diameter 63 of theaft mating ring 34. The pressure decay toward the top of the aft face 49could result from flow conditions into the low pressure region near theouter diameter surface 51. The pressure decay along the aft face 49immediately adjacent to the annular gap 40 could result from flow intothe channel 53 along the inner diameter surface 52.

The resultant force balance acting along the opposed aft and forwardfaces 49, 50 allows the piston ring 35 to rotate without contacting theforward and aft mating rings 33, 34. In preferred embodiments, the forcebalance centers the piston ring 35 so as to be equidistant from theforward and aft mating rings 33, 34. Any excursions from thesteady-state position of the piston ring 35 increase the interfacepressure, thus restoring the piston ring 35 to its steady-state positionwithin the seal system 29. The substantially symmetric aft pressureprofile 57 minimizes pressure induced twist imparted by thenon-symmetric forward pressure profile 58.

Referring now to FIGS. 12 a-12 d, the seal system 29 in FIG. 11 a is nowshown including a plurality of divergent flow grooves 47 disposed alongthe face 42 of the forward mating ring 33 and along the face 41 of theaft mating ring 34. The divergent flow grooves 47 are positioned alongthe aft and forward mating rings 33, 34 so as to overlay the piston ring35. In preferred embodiments, the divergent flow grooves 47 along theforward and aft mating rings 33, 34 are disposed so that the apexes 48are at the same radial distance from the centerline of the inner shaft31. In other embodiments, the divergent flow grooves 47 could beprovided along the forward mating ring 33 only and other hydrodynamicgrooves along the aft mating ring 34.

The forward mating ring 33 could include a plurality of ports 46disposed circumferentially about and through the forward mating ring 33.Ports 46 are positioned adjacent to the divergent flow grooves 47 so asto communicate fluid from the high pressure region onto the apexes 48,as represented in FIG. 12 a. In some embodiments, one or more ports 46could be positioned forward of each apex 48 so that the fluid exitingthe ports 46 passes into the divergent flow grooves 47 via the relativerotation between the forward mating ring 33 and piston ring 35. Inpreferred embodiments, at least one port 46 could be positioned withinthe apex 48 so as to directly communicate fluid from the high pressureregion into the divergent flow groove 47 which is then separated intotwo flows along the grooves 27, 28, as represented in FIGS. 12 c and 12d. The divergent flow grooves 47 disposed along the face 41 of the aftmating ring 34 are as shown in FIG. 11 d.

The aft mating ring 34 could include a plurality of ports 61 disposedcircumferentially about and through the aft mating ring 34. The ports 61could be positioned along the aft mating ring 34 between the piston ring35 and spacer ring 36 so as to vent fluid from the annular gap 40 intothe low pressure region.

Referring now to FIGS. 12 e and 12 f, the piston ring 35 is shownincluding a channel 53 which directs fluid along the outer diametersurface 51 downward and out from an outlet 62 along the aft face 49. Thechannel 53 is shown as an L-shaped structure; however, other designs arepossible. The piston ring 35 could include one or more circumferentialgrooves 19 along the corner between the forward face 50 and the outerdiameter surface 51 so as to improve flow into the channels 35. Thegrooves 19 could partially traverse the thickness of the piston ring 35so as to maintain a dam 65 along the outer diameter surface 51 adjacentto the lower pressure region. The dam 65 could restrict flow over thepiston ring 35 adjacent to an outer shaft. In some embodiments, thegrooves 19 could be circumferentially disposed along the central regionof the outer diameter surface of the piston ring 35 and include aplurality of feed slots from a face along the piston ring 35 whichintersect the groove 19 so as to allow fluid to enter the groove 19. Theoutlet 62 for each channel 53 is positioned along the aft face 49 so asto communicate fluid onto the apex 48 of each divergent flow groove 47along the face 41. One or more outlets 62 could be positioned along oneor more arcuate-shaped grooves 55 along the piston ring 35 so as tofocus and/or direct flow from the channels 53 onto one or more apexes 48as the aft mating ring 34 rotates relative to the piston ring 35.

Referring now to FIG. 12 g, an exemplary flow diagram is showndescribing one possible steady-state flow pattern between the high andlow pressure regions over the seal system 29 in FIG. 12 a.

In this embodiment, the fluid from the high pressure region passes overthe forward mating ring 33 and into the grooves 19 at the top of thepiston ring 35. Thereafter, the fluid traverses the channels 53 so as toexit the outlets 62 immediately adjacent to the divergent flow grooves47 along the aft mating ring 34. The fluid then enters the divergentflow grooves 47 via the apexes 48 and is separated into the grooves 27,28. The divergent flow grooves 47 then communicate a substantiallysymmetric pressure force onto the aft face 49 of the piston ring 35.

Fluid from the high pressure region also passes through the ports 46 andinto the space between the forward mating ring 33 and piston ring 35.The fluid then passes onto apexes 48 of the divergent flow grooves 47along the forward mating ring 33 where it is separated into the grooves27, 28. Thereafter, the fluid is communicated onto the forward face 50of the piston ring 35 as a substantially symmetric pressure force.

A portion of the fluid which passes downward between the forward matingring 33 and piston ring 35 enters the annular gap 40 between the pistonring 35 and spacer ring 36 and combines with a portion of the fluidpassing downward between the aft mating ring 34 and piston ring 35before entering the low pressure region via the ports 61. A portion ofthe fluid which passes upward between the forward mating ring 33 andpiston ring 35 combines with fluid passing over the forward mating ring33 and enters the channels 53. A portion of the fluid which passesupward between the aft mating ring 34 and the piston ring 35 passes overthe aft mating ring 34 into the low pressure region.

Referring now to FIG. 12 h, an exemplary pressure diagram is showndescribing the steady-state pressures along the aft face 49, forwardface 50, outer diameter surface 51, and inner diameter surface 52 of thepiston ring 35 in FIG. 12 a.

The pressure along the inner diameter surface 52 is produced primarilyby the fluid within the annular gap 40 and generally negligible as it isvented into the low pressure region via the ports 61. The outer diameterpressure profile 59 could result from the outward centrifugal forcesacting along the piston ring 35 as it presses against the outer shaft32, pressure force acting along the inner diameter surface 52, andpressure forces acting along the outer diameter surface 51 within thegroove 19. The outer diameter pressure profile 59 is generally uniformwith a gradual decay toward the aft face 49. This decay is attributed toflow into the low pressure region immediately adjacent to the aft matingring 34 near the outer diameter surface 51. The resultant force balancefixes the piston ring 35 to the outer shaft 32 so that both rotatewithout sliding.

The forward pressure profile 58 results primarily from the hydrodynamicforces imposed onto the forward face 50 of the piston ring 35 by thedivergent flow grooves 47. The forward pressure profile 58 issubstantially symmetric about the apexes 48 of the divergent flowgrooves 47. Flow from the high pressure region results in a more uniformpressure profile adjacent to the grooves 19.

The aft pressure profile 57 results primarily from the hydrodynamicforces imposed onto the aft face 49 of the piston ring 35 by thedivergent flow grooves 47. The aft pressure profile 57 is substantiallysymmetric about the apexes 48 of the divergent flow grooves 47.

Any asymmetries along the aft and forward pressure profiles 57, 58 aredue in part to asymmetries along the grooves 27, 28 about the apex 48 orventing conditions adjacent to the outer and inner diameter surfaces 51,52. The pressure generally increases with distance from the apexes 48because orientation of the divergent flow grooves 47 biases the flowpattern from the apexes 48 towards the grooves 27, 28. The maximumpressure along the aft and forward pressure profiles 57, 58 could occurnear the ends of the grooves 27, 28, or one or both ends of the pistonring 35, or near the outer diameter 63 of the aft mating ring 34. Thepressure decay beyond the maximums could result from venting conditionsadjacent to the annular gap 40 and the aft face 49 near the outerdiameter surface 51.

The resultant force balance acting along the opposed aft and forwardfaces 49, 50 allows the piston ring 35 to rotate without contacting theforward and aft mating rings 33, 34. In preferred embodiments, the forcebalance centers the piston ring 35 so as to be equidistant from theforward and aft mating rings 33, 34. Any excursions from thesteady-state position of the piston ring 35 increase the interfacepressure, thus restoring the piston ring 35 to its steady-state positionwithin the seal system 29. The substantially symmetric aft and forwardpressure profiles 57, 58 minimize pressure induced twisting along thepiston ring 35.

Referring now to FIGS. 12 i and 12 j, the piston ring 35 shown in FIGS.12 a-12 h now includes a plurality of channels 53 horizontally disposedso as to traverse the thickness of the piston ring 35. In thisembodiment, the channels 53 are shown as linear structures; however,other designs are possible. The channels 53 are positioned along thepiston ring 35 so as to at least partially align with the ports 46 alongthe forward mating ring 33 and the apexes 48 of the divergent flowgrooves 47 along the forward and aft mating rings 33, 34. Thisarrangement allows the channels 53 to direct fluid from the highpressure region directly onto the divergent flow grooves 47 along theaft mating ring 34. The piston ring 35 could include one or morecircumferential grooves 19 as described. The grooves 19 could partiallytraverse the thickness of the piston ring 35 so as to form a dam 65along the outer diameter surface 51 adjacent to the high pressureregion. This arrangement restricts flow from passing over the pistonring 35 adjacent to an outer shaft and reduces the total magnitude ofthe outer diameter pressure profile 59.

Referring again to FIG. 12 i, an exemplary flow diagram is showndescribing one possible steady-state flow pattern between the high andlow pressure regions about the piston ring 35 with forward facing dam65.

In this embodiment, fluid from the high pressure region passes over theforward mating ring 33 and is directed between the piston ring 35 andforward mating ring 33 via the dam 65. Fluid also traverses the ports 46along the forward mating ring 33 and enters the space between the pistonring 35 and forward mating ring 33. The fluid is communicated onto thedivergent flow grooves 47 where it is separated into the grooves 27, 28which then communicate a substantially symmetric pressure force onto theforward face 50 of the piston ring 35.

A portion of the fluid from the high pressure region then passes throughthe channels 53 and into the space between the aft mating ring 34 andpiston ring 35. This fluid enters the apexes 48 of the divergent flowgrooves 47 along the aft mating ring 34 where it is separated into thegrooves 27, 28. Thereafter, the fluid is communicated onto the aft face49 of the piston ring 35 as a substantially symmetric pressure force.

Another portion of the fluid passes through the annular gap 40 betweenthe piston ring 35 and the spacer ring 36. This fluid then mixes with aportion of the fluid from the channels 53 and is then vented into thelow pressure regions via the ports 61. The remaining portion of thefluid from the channels 53 passes over the aft mating ring 34 and intothe low pressure region.

Referring again to FIG. 12 j, an exemplary pressure diagram is showndescribing the steady-state pressures along the aft face 49, forwardface 50, outer diameter surface 51, and inner diameter surface 52 of thepiston ring 35 with forward facing dam 65.

The pressure along the inner diameter surface 52 is produced primarilyby fluid within the annular gap 40 and generally negligible as it isvented into the low pressure region via the ports 61. The outer diameterpressure profile 59 could result from the outward centrifugal forcesacting along the piston ring 35 as it presses against the outer shaft32, pressure forces acting along the inner diameter surface 52, andpressure induced forces acting along the outer diameter surface 51. Theouter diameter pressure profile 59 is generally non-uniform with a rapiddecay toward the aft face 49. The magnitude of the outer diameterpressure profile 59 and its decay result primarily from the centrifugalforces which are influenced by the thickness of the dam 65. The dam 65prevents fluid from contacting the outer diameter surface 51, thusavoiding fluid induced pressure forces along the outer diameter surface51. The resultant force balance fixes the piston ring 35 to the outershaft 32 so that both rotate without sliding.

The forward pressure profile 58 results primarily from the hydrodynamicforces imposed onto the forward face 50 of the piston ring 35 by thedivergent flow grooves 47. The forward pressure profile 58 issubstantially symmetric about the apexes 48 of the divergent flowgrooves 47. Flow from the high pressure region onto the forward matingring 33 results in a uniform pressure profile adjacent to the dam 65.

The aft pressure profile 57 results primarily from the hydrodynamicforces imposed onto the aft face 49 of the piston ring 35 by thedivergent flow grooves 47. The aft pressure profile 57 is substantiallysymmetric about the apexes 48 of the divergent flow grooves 47.

Any asymmetries along the aft and forward pressure profiles 57, 58 aredue in part to asymmetries along the grooves 27, 28 about the apex 48 orventing conditions adjacent to the outer and inner diameter surfaces 51,52. The pressure generally increases with distance from the apexes 48because orientation of the divergent flow grooves 47 biases the flowpattern from the apexes 48 towards the grooves 27, 28. The maximumpressure along the aft and forward pressure profiles 57, 58 could occurnear the ends of the grooves 27, 28, or one or both ends of the pistonring 35, or near the outer diameter 63 of the aft mating ring 34. Thepressure decay beyond the maximums could result from venting conditionsadjacent to the annular gap 40 and the aft face 49 near the outerdiameter surface 51.

The resultant force balance acting along the opposed aft and forwardfaces 49, 50 allows the piston ring 35 to rotate without contacting theforward and aft mating rings 33, 34. In preferred embodiments, the forcebalance centers the piston ring 35 so as to be equidistant from theforward and aft mating rings 33, 34. Any excursions from thesteady-state position of the piston ring 35 increase the interfacepressure, thus restoring the piston ring 35 to its steady-state positionwithin the seal system 29. The substantially symmetric aft and forwardpressure profiles 57, 58 minimize pressure induced twisting along thepiston ring 35.

Referring now to FIGS. 11 i and 11 j, the dam 65 from in FIG. 12 i islikewise applicable to the piston ring 35 shown in FIGS. 11 a-11 h. Inthis embodiment, the piston ring 35 could include one or morecircumferential grooves 19 as described herein. The grooves 19 couldpartially traverse the thickness of the piston ring 35 so as to form adam 65 along the outer diameter surface 51 adjacent to the high pressureregion. This arrangement could restrict flow over the piston ring 35adjacent to an outer shaft and reduce the total magnitude of the outerdiameter pressure profile 59.

The outer diameter pressure profile 59 could result from the outwardcentrifugal forces acting along the piston ring 35 as it presses againstthe outer shaft 32, pressure forces acting along the inner diametersurface 52, and pressure induced forces acting along the outer diametersurface 51. The outer diameter pressure profile 59 is generallynon-uniform with a rapid decay toward the aft face 49. The magnitude ofthe outer diameter pressure profile 59 and its decay result primarilyfrom the centrifugal forces which are influenced by the thickness of thedam 65. The dam 65 prevents fluid from contacting the outer diametersurface 51, thus avoiding fluid induced pressure forces along the outerdiameter surface 51. The resultant force balance fixes the piston ring35 to the outer shaft 32 so that both rotate without sliding. Pressureforces along the forward and aft faces 50, 49 are substantially asdescribed in FIG. 11 h.

Referring now to FIGS. 13 a-13 d, the seal system 29 in FIG. 11 a is nowshown including a piston ring 35 with a plurality of downward flowchannels 53 interposed between a forward mating ring 33 with outwardflow hydrodynamic grooves 43 and an aft mating ring 34 with divergentflow grooves 47.

The piston ring 35 is shown including a channel 53 which directs fluidalong the outer diameter surface 51 downward and out from an outlet 62along the aft face 49. The channel 53 is shown as an L-shaped structure;however other designs are possible. The piston ring 35 could include oneor more circumferential grooves 19 along the corner between the forwardface 50 and the outer diameter surface 51 forming a dam 65 adjacent tothe low pressure region, as otherwise described herein, so as to improveflow into the channels 35, as represented in FIGS. 13 d and 12 f. Theoutlet 62 is positioned along the aft face 49 so as to communicate fluidonto the apex 48 of each divergent flow groove 47 along the face 41. Oneor more outlets 62 could be positioned along one or more arcuate-shapedgrooves 55 along the piston ring 35 so as to focus and/or direct flowfrom the channels 53 onto one or more apexes 48 as the aft mating ring34 rotated relative to the piston ring 35.

The aft mating ring 34 could include a plurality of ports 61 disposedcircumferentially about and through the aft mating ring 34. The ports 61could be positioned along the aft mating ring 34 between the piston ring35 and spacer ring 36 so as to vent fluid from the annular gap 40 intothe low pressure region.

Referring now to FIG. 13 d, an exemplary flow diagram is showndescribing one possible steady-state flow pattern between the high andlow pressure regions over the seal system 29 in FIG. 13 a.

In this embodiment, the fluid from the high pressure region passes overthe forward mating ring 33 and into the grooves 19 at the top of thepiston ring 35. Thereafter, the fluid traverses the channels 53 so as toexit the outlets 62 immediately adjacent to the divergent flow grooves47 along the face 41 of the aft mating ring 34. The fluid then entersthe divergent flow grooves 47 via the apexes 48 and is separated intothe grooves 27, 28 described herein. The divergent flow grooves 47 thencommunicate a substantially symmetric pressure force onto the aft face49 of the piston ring 35.

Fluid from the high pressure region also passes down between the spacebetween the forward mating ring 33 and piston ring 35 and over theoutward flow hydrodynamic grooves 43. Thereafter, the fluid enters theannular gap 40 between the piston ring 35 and spacer ring 36.

A portion of the fluid which passes downward between the aft mating ring34 and the piston ring 35 enters the annular gap 40 and combines withthe fluid which passes downward between the forward mating ring 33 andpiston ring 35 before entering the low pressure region via the ports 61.A portion of the fluid which passes upward between the aft mating ring34 and the piston ring 35 passes over the aft mating ring 34 into thelow pressure region.

Referring now to FIG. 13 e, an exemplary pressure diagram is showndescribing the steady-state pressures along the aft face 49, forwardface 50, outer diameter surface 51, and inner diameter surface 52 of thepiston ring 35 in FIG. 13 a.

The pressure along the inner diameter surface 52 is produced primarilyby the fluid within the annular gap 40 and generally negligible as it isquickly vented into the low pressure region via the ports 61. The outerdiameter pressure profile 59 could result from the outward centrifugalforces acting along the piston ring 35 as it presses against the outershaft 32, pressure force acting along the inner diameter surface 52, andpressure forces acting along the outer diameter surface 51 within thegroove 19. The outer diameter pressure profile 59 is generally uniformwith a gradual decay toward the aft face 49. This decay is attributed toflow into the low pressure region immediately adjacent to the aft matingring 34 near the outer diameter surface 51. The resultant force balancefixes the piston ring 35 to the outer shaft 32 so that both rotatewithout sliding.

The forward pressure profile 58 results primarily from the hydrodynamicforces imposed along the piston ring 35 immediately adjacent to theforward face 50 via the outward flow hydrodynamic grooves 43. Theprofile is generally triangular-shaped and non-symmetric becausepressures within a groove generally increase along the direction offlow.

The aft pressure profile 57 results primarily from the hydrodynamicforces imposed onto the aft face 49 of the piston ring 35 by thedivergent flow grooves 47. The aft pressure profile 57 is substantiallysymmetric about the apexes 48 of the divergent flow grooves 47.

Any asymmetries along the aft and forward pressure profiles 57, 58 aredue in part to asymmetries along the grooves 27, 28 about the apex 48 orventing conditions adjacent to the outer and inner diameter surfaces 51,52. The pressure generally increases away from the apexes 48 becauseorientation of the divergent flow grooves 47 biases flow from the apexes48 towards the grooves 27, 28. The maximum pressure along the aft andforward pressure profiles 57, 58 could occur near the ends of thegrooves 27, 28, or one or both ends of the piston ring 35, or near theouter diameter 63 of the aft mating ring 34. The pressure decay beyondthe maximums could result from venting conditions adjacent to theannular gap 40 and the outer diameter surface 51 at the aft face 49.

The resultant force balance acting along the opposed aft and forwardfaces 49, 50 allows the piston ring 35 to rotate without contacting theforward and aft mating rings 33, 34. In preferred embodiments, the forcebalance centers the piston ring 35 so as to be equidistant from theforward and aft mating rings 33, 34. Any excursions from thesteady-state position of the piston ring 35 cause an increase in theinterface pressure, thus restoring the piston ring 35 to itssteady-state position within the seal system 29. The substantiallysymmetric aft pressure profile 57 minimizes pressure induced twistingimposed by the forward mating ring 33.

The divergent flow grooves 47 and outward flow hydrodynamic grooves 43described herein are understood to include depressions, recesses, orslots disposed along the surface of the forward and aft mating rings 33,34. In some embodiments, the depth and width of the divergent flowgrooves 47 and outward flow hydrodynamic grooves 43 are uniform orconstant.

Referring now to FIGS. 14 a and 14 b, the divergent flow grooves 47could include variable depths and widths. For example, the divergentflow groove 47 in FIG. 14 a is shown including grooves 27, 28 each withan inwardly tapered profile (W₁ to W₂) from the apex 48 to the end ofeach groove 27, 28. In another example, the divergent flow groove 47 inFIG. 14 b is shown with a depth profile (D₁ to D₂) that decreases withdistance from the apex 48.

Referring now to FIGS. 15 a and 15 b, the hydrodynamic grooves describedherein, as well as other grooves capable of imparting a non-symmetricpressure profile onto a piston ring 35, could also include variabledepths and widths. For example, the hydrodynamic groove 64 in FIG. 15 ais shown with a tapered profile from W₁ to W₂ against the direction ofrotation. In another example, the hydrodynamic groove 64 in FIG. 15 b isshown with a depth profile that decreases from D₁ to D₂ against thedirection of rotation.

Referring now to FIGS. 16 a-16 c, the seal system 29 is now shownincluding a plurality of divergent flow grooves 47 disposed along theface 42 of the forward mating ring 33 and along the face 41 of the aftmating ring 34. The divergent flow grooves 47 are positioned along theforward and aft mating rings 33, 34 so as to overlay the piston ring 35.In preferred embodiments, the divergent flow grooves 47 along theforward and aft mating rings 33, 34 are disposed so that the apexes 48are at the same radial distance from the centerline of the inner shaft31. The apex 48 is positioned toward the direction of rotation. Theforward and aft mating rings 33, 34 and spacer ring 36 contact a carrier37 about an inner shaft 31, shown in FIG. 6, and are secured thereto viaa stop ring 54 so as to be rotatable with the inner shaft 31.

The aft mating ring 34 could include a plurality of ports 61 disposedcircumferentially about and through the aft mating ring 34. The ports 61could be positioned along the aft mating ring 34 between the piston ring35 and spacer ring 36 so as to vent fluid from the annular gap 40 intothe low pressure region.

Referring now to FIGS. 16 d-16 f, the piston ring 35 is shown includinga channel 53 which directs fluid along the outer diameter surface 51downward and out from outlets 62 along the aft and forward faces 49, 50.The channel 53 is shown as a generally T-shaped structure comprised of asubstantially vertical channel intersecting a substantially horizontalchannel thereby providing a continuous pathway. The piston ring 35 couldinclude one or more circumferential grooves 19 along the corner betweenthe forward face 50 and the outer diameter surface 51 so as to improveflow into the channels 53. The grooves 19 could partially traverse thethickness of the piston ring 35 so as to maintain a dam 65 along theouter diameter surface 51 adjacent to the lower pressure region. The dam65 could restrict flow over the piston ring 35 adjacent to an outershaft 32. In some embodiments, the grooves 19 could be circumferentiallydisposed along the central region of the outer diameter surface of thepiston ring 35 and include a plurality of feed slots from a face alongthe piston ring 35 adjacent to the higher pressure region whichintersect the groove 19 so as to allow fluid to enter the groove 19, asrepresented in FIGS. 16 d-16 f. The outlets 62 for each channel 53 arepositioned along the aft and forward faces 49, 50 so as to communicatefluid onto the apex 48 of each divergent flow groove 47 along the faces41, 42. One or more outlets 62 could be positioned along one or morearcuate-shaped grooves 55 along the piston ring 35 so as to focus and/ordirect flow from the channels 53 onto one or more apexes 48 as the aftmating ring 34 rotates relative to the piston ring 35.

Referring now to FIG. 16 g, an exemplary flow diagram is showndescribing one possible steady-state flow pattern between the high andlow pressure regions over the seal system 29 in FIG. 16 a.

The fluid from the high pressure region passes over the forward matingring 33 and into the grooves 19 at the top of the piston ring 35.Thereafter, the fluid enters and traverses the channels 53 so as to exitthe outlets 62 immediately adjacent to the divergent flow grooves 47along the forward and aft mating rings 33, 34. The fluid then enters thedivergent flow grooves 47 via the apexes 48 and is separated into thegrooves 27, 28. The divergent flow grooves 47 then communicate asubstantially symmetric pressure force onto the aft and forward faces49, 50 of the piston ring 35.

A portion of the fluid which passes downward between the forward matingring 33 and piston ring 35 enters the annular gap 40 between the pistonring 35 and spacer ring 36 and combines with a portion of the fluidpassing downward between the aft mating ring 34 and piston ring 35before entering the low pressure region via the ports 61. A portion ofthe fluid which passes upward between the forward mating ring 33 andpiston ring 35 combines with fluid passing over the forward mating ring33 and reenters the channels 53. A portion of the fluid which passesupward between the aft mating ring 34 and the piston ring 35 passes overthe aft mating ring 34 into the low pressure region.

Referring now to FIG. 16 h, an exemplary pressure diagram is showndescribing the steady-state pressures along the aft face 49, forwardface 50, outer diameter surface 51, and inner diameter surface 52 of thepiston ring 35 in FIG. 16 a.

The pressure along the inner diameter surface 52 is produced primarilyby the fluid within the annular gap 40 and generally negligible as it isvented into the low pressure region via the ports 61. The outer diameterpressure profile 59 could result from the outward centrifugal forcesacting along the piston ring 35 as the piston ring 35 presses againstthe outer shaft 32, pressure force acting along the inner diametersurface 52, and pressure forces acting along the outer diameter surface51 within the groove 19. The outer diameter pressure profile 59 isgenerally uniform with a gradual decay toward the aft face 49. Thisdecay is attributed to flow into the low pressure region immediatelyadjacent to the aft mating ring 34 near the outer diameter surface 51.The resultant force balance fixes the piston ring 35 to the outer shaft32 so that both rotate without sliding.

The forward pressure profile 58 results primarily from the hydrodynamicforces imposed onto the forward face 50 of the piston ring 35 by thedivergent flow grooves 47 along the forward mating ring 33. The forwardpressure profile 58 is substantially symmetric about the apexes 48 ofthe divergent flow grooves 47.

The aft pressure profile 57 results primarily from the hydrodynamicforces imposed onto the aft face 49 of the piston ring 35 by thedivergent flow grooves 47 along the aft mating ring 34. The aft pressureprofile 57 is substantially symmetric about the apexes 48 of thedivergent flow grooves 47.

Any asymmetries along the aft and forward pressure profiles 57, 58 aredue in part to asymmetries along the grooves 27, 28 about the apex 48 orventing conditions adjacent to the outer and inner diameter surfaces 51,52. The pressure generally increases with distance from the apexes 48because orientation of the divergent flow grooves 47 biases the flowpattern from the apexes 48 towards the grooves 27, 28. The maximumpressure along the aft and forward pressure profiles 57, 58 could occurnear the ends of the grooves 27, 28, or one or both ends of the pistonring 35, or near the outer diameter 63 of the aft mating ring 34. Thepressure decay beyond the maximums could result from venting conditionsadjacent to the annular gap 40 and the aft and forward faces 49, 50 nearthe outer diameter surface 51.

The resultant force balance acting along the opposed aft and forwardfaces 49, 50 allows the piston ring 35 to rotate without contacting theforward and aft mating rings 33, 34. In preferred embodiments, the aftand forward pressure profiles 57, 58 are substantially balanced therebycentering the piston ring 35 so as to be approximately equidistant fromthe forward and aft mating rings 33, 34. Any excursions from thesteady-state position of the piston ring 35 increase the interfacepressure along one side of the piston ring 35, thus restoring the pistonring 35 to its steady-state position within the seal system 29. Thesubstantially symmetric aft and forward pressure profiles 57, 58minimize pressure induced twist along the piston ring 35.

Referring now to FIGS. 17 a-17 c, the seal system 29 is shown includinga piston ring 35 interposed between a forward mating ring 33 and an aftmating ring 34. A spacer ring 36 is arranged concentrically with thepiston ring 35. The spacer ring 36 is wider than the piston ring 35 soas to contact the forward and aft mating rings 33, 34, thereby allowingthe piston ring 35 to translate between the mating rings 33, 34. Theforward and aft mating rings 33, 34 and spacer ring 36 contact a carrier37 about an inner shaft 31, shown in FIG. 6, and are secured thereto viaa stop ring 54 so as to be rotatable with the inner shaft 31. Theforward and aft mating rings 33, 34 include grooves disposed along asurface immediately adjacent to the piston ring 35.

The piston ring 35 is dimensioned to have an inner diameter larger thanthe outer diameter of the spacer ring 36 so as to form an annular gap 40therebetween. The piston ring 35 is also preferred to have an outerdiameter which either avoids or limits contact with the inner diameterof the outer shaft 32 when the outer shaft 32 is at rest. The pistonring 35 also includes one or more design features known within the art,one example being the gap 56 shown in FIGS. 17 e and 17 f, which allowthe piston ring 35 to flex or expand diametrically so as to contact theouter shaft 32 as the piston ring 35 and outer shaft 32 rotate. Thecontact forces between the piston ring 35 and outer shaft 32 should besufficient so that the piston ring 35 moves with the outer shaft 32while avoiding and/or minimizing friction-induced wear therebetween.Also, contact between the piston ring 35 and outer shaft 32 is preferredto restrict fluid from flowing directly from the high pressure region tothe low pressure region.

A plurality of divergent flow grooves 47 could be provided along theface 41 of the aft mating ring 34 and the face 42 of the forward matingring 33. The divergent flow grooves 47 are located along the faces 41,42 so as to overlay at least a portion of the radial width (W_(P)) ofthe piston ring 35, preferably overlaying the piston ring 35 duringtransient and steady-state operations of the turbine. This arrangementensures that the divergent flow grooves 47 communicate a hydrodynamicforce onto the piston ring 35 regardless of its position between themating rings 33, 34 and/or inner and outer shafts 31, 32.

As shown in FIG. 6, the forward and aft mating rings 33, 34 each have anouter diameter less than the inner diameter of the outer shaft 32. Theresultant spaces allow fluid to flow out of the high pressure region andinto the low pressure region. In some embodiments, a plurality of ports46 could be disposed through the forward mating ring 33 adjacent to thecarrier 37, however positioned so as to communicate fluid to the annulargap 40 between the piston ring 35 and spacer ring 36, as represented inFIGS. 17 a-17 c. The ports 46 could be cylindrical-shaped holes whichextend from the high pressure region through to the annular gap 40. Theports 46 are disposed along the face 42 of the forward mating ring 33 atone or more radial distances from the centerline of the inner shaft 31.One or more ports 46 could be aligned immediately adjacent to eachdivergent flow groove 47.

Each divergent flow groove 47 could include a pair of grooves 27, 28disposed along the face 41 of the aft mating ring 34, as described inFIG. 12 d. The grooves 27, 28 are aligned in an intersecting fashion soas to form an apex 48. The grooves 27, 28 could include linear and/orarcuate-shaped shallow depressions or slots. The grooves 27, 28 arepreferred to be aligned symmetrically about the apex 48. The divergentflow grooves 47 are preferred to be aligned with the apexes 48 pointingtoward the direction of rotation so that fluid entering each apex 48 isdirected into the corresponding grooves 27, 28 resulting in the flowsgraphically represented in FIG. 11 d. The dimensions, shape, andalignment of the apex 48 and grooves 27, 28 should ensure that fluidentering the apex 48 is separated into two flows. The flows should be atleast substantially equal so as to communicate a substantially symmetricpressure profile about the axis of symmetry defined by the apex 48 andgrooves 27, 28.

In some embodiments, divergent flow grooves 47 could be aligned aboutthe aft mating ring 34 so that one or more apexes 48 are disposedbetween each pair of grooves 27, 28. For example, FIG. 11 d showsdivergent flow grooves 47 whereby one apex 48 from a neighboringdivergent flow groove 47 resides between each paired arrangement ofgrooves 27, 28. In other embodiments, the divergent flow grooves 47could be arranged end-to-end without overlap so that the apex 48 of eachdivergent flow groove 47 begins immediately or some distance from theend of the adjacent grooves 27, 28.

In order for the divergent flow grooves 47 to produce substantiallysymmetric pressures along at least a portion of the radial width (W_(P))of the piston ring 35, fluid is communicated onto each divergent flowgroove 47 so as to impinge at least a portion of the apex 48, thusallowing the resultant flow to be approximately equally divided betweenthe grooves 27, 28.

Referring now to FIGS. 17 d-17 f, the piston ring 35 could include aplurality of channels 53 which direct fluid from the annular gap 40upward through the piston ring 35. In FIG. 17 d, the piston ring 35 isshown with a generally T-shaped channel 53, with a generally circularcross section, which forms a complete passage from the inner diametersurface 52 to the outlets 62 along the aft face 49 and forward face 50.The channel 53 is comprised of a substantially vertical channelintersecting a substantially horizontal channel thereby providing acontinuous pathway. The channels 53 are separately disposed about thepiston ring 35 in a circumferential fashion, as represented in FIG. 17e, at a radius which ensures fluid exiting the channel 53 via theoutlets 62 along the aft face 49 impinges the apexes 48 immediatelyadjacent thereto along the aft mating ring 34 and fluid exiting thechannel 53 via the outlets 62 along the forward face 50 impinges theapexes 48 immediately adjacent thereto along the forward mating ring 33.In preferred embodiments, the centers of each outlet 62 and each apex 48should be at about the same radial distance from the centerline of theinner shaft 31.

One or more generally arcuate-shaped grooves 55 could be included alongthe forward and aft faces 50, 49 of the piston ring 35. Each groove 55could be a pocket recessed along the piston ring 35 about one or moreoutlets 62. The radial position of the grooves 55 could overlay theapexes 48 along the forward and aft mating rings 33, 34. The length ofeach groove 55 could be sufficient so as to overlap one or more apexes48 as the piston ring 35 rotates with respect to the aft mating ring 34.This arrangement allows the fluid communicated through a channel 53 toexit the piston ring 35 into at least one groove 55 prior tocommunication onto one or more apexes 48 disposed along the aft matingring 34.

Referring now to FIG. 17 g, an exemplary flow diagram describes onepossible steady-state flow pattern between the high and low pressureregions over the seal system 29 in FIG. 17 a. The fluid from the highpressure region passes over the forward mating ring 33 adjacent to theouter shaft 32 and through the forward mating ring 33 via the ports 46.The fluid passing over the forward mating ring 33 may be directeddownward, because of the contact between piston ring 35 and outer shaft32, along the space between the forward mating ring 33 and piston ring35. The fluid passing through the ports 46 enters the annular gap 40 andis directed into the channel 53. The fluid traverses the channel 53 andexits the outlets 62 immediately adjacent to the divergent flow grooves47 along the forward and aft mating rings 33, 34. The fluid then entersthe divergent flow grooves 47 via the apexes 48 and is separated intothe grooves 27, 28. The divergent flow grooves 47 then communicate asubstantially symmetric pressure force onto the aft and forward faces49, 50 of the piston ring 35.

A portion of the fluid which passes downward between the forward matingring 33 and piston ring 35 enters the annular gap 40 between the pistonring 35 and spacer ring 36 and combines with a portion of the fluidpassing downward between the aft mating ring 34 and piston ring 35before reentering the channel 53 with fluid from the ports 46. A portionof the fluid which passes upward between the forward mating ring 33 andpiston ring 35 combines with fluid passing over the forward mating ring33. This fluid could be redirected downward between the forward matingring 33 and the piston ring 35 in some applications. A portion of thefluid which passes upward between the aft mating ring 34 and the pistonring 35 passes over the aft mating ring 34 into the low pressure region.

Referring now to FIG. 17 h, an exemplary pressure diagram describes thesteady-state pressures along the aft face 49, forward face 50, outerdiameter surface 51, and inner diameter surface 52 of the piston ring 35in FIG. 17 a.

The inner diameter pressure profile 60 is produced by the fluid withinthe annular gap 40 and is generally uniform along the inner diametersurface 52. The outer diameter pressure profile 59 could result from theoutward centrifugal forces acting along the piston ring 35 as it pressesagainst the outer shaft 32 and forces acting along the inner diametersurface 52. The outer diameter pressure profile 59 is generallynon-linear because of the flow pattern into the low pressure regionimmediately adjacent to the aft mating ring 34 near the outer diametersurface 51. The resultant force balance fixes the piston ring 35 to theouter shaft 32 so that both rotate together without sliding.

The forward pressure profile 58 results primarily from the hydrodynamicforces imposed along the piston ring 35 immediately adjacent to theforward face 50 via the divergent flow grooves 47. The forward pressureprofile 58 is substantially symmetric about the apexes 48 of thedivergent flow grooves 47.

The aft pressure profile 57 results primarily from the hydrodynamicforces imposed onto the aft face 49 of the piston ring 35 by thedivergent flow grooves 47. The aft pressure profile 57 is substantiallysymmetric about the apexes 48 of the divergent flow grooves 47.

Any asymmetries along the aft pressure profile 57 are due in part toasymmetries along the grooves 27, 28 about the apex 48 or ventingconditions along the aft face 49 adjacent to the outer and innerdiameter surfaces 51, 52. The pressure generally increases with distancefrom the apex 48 because orientation of the divergent flow grooves 47direct the flow pattern from the apex 48 towards the grooves 27, 28. Themaximum pressure could occur near the ends of grooves 27, 28, or one orboth ends of the piston ring 35, or near the outer diameter 63 of theaft mating ring 34. The pressure decay toward the top of the aft face 49could result from flow conditions into the low pressure region near theouter diameter surface 51. The pressure decay along the aft face 49immediately adjacent to the annular gap 40 could result from flow intothe channel 53 along the inner diameter surface 52.

The resultant force balance acting along the opposed aft and forwardfaces 49, 50 allows the piston ring 35 to rotate without contacting theforward and aft mating rings 33, 34. In preferred embodiments, the forcebalance centers the piston ring 35 so as to be approximately equidistantfrom the forward and aft mating rings 33, 34. Any excursions from thesteady-state position of the piston ring 35 increase the interfacepressure adjacent to the excursion, thus restoring the piston ring 35 toits steady-state position within the seal system 29. The substantiallysymmetric aft pressure profile 57 minimizes pressure induced twistimparted by the non-symmetric forward pressure profile 58.

Referring now to FIG. 17 i, a dam 65 could be provided toward the outerdiameter of the piston ring 35. The dam 65 could be formed by grooves 19along the outer diameter of the piston ring 35. This arrangement couldrestrict flow over the piston ring 35 adjacent to an outer shaft andreduce the total magnitude of the outer diameter pressure profile 59.The resultant pressure profile would break down over a smaller arearather than over the entire thickness of the piston ring 35. Flowpatterns about the piston ring 35 are as described in FIG. 17 g.

Referring now to FIG. 17 j, an exemplary pressure diagram describes thesteady-state pressures along the aft face 49, forward face 50, outerdiameter surface 51, and inner diameter surface 52 of the piston ring 35in FIG. 17 i. The outer diameter pressure profile 59 could result fromthe outward centrifugal forces acting along the piston ring 35 as itpresses against the outer shaft 32, pressure forces acting along theinner diameter surface 52, and pressure induced forces acting along theouter diameter surface 51. The outer diameter pressure profile 59 isgenerally non-uniform with a rapid decay toward the aft face 49. Themagnitude of the outer diameter pressure profile 59 and its decay resultprimarily from the centrifugal forces which are influenced by thethickness of the dam 65. The dam 65 prevents fluid from contacting theouter diameter surface 51, thus avoiding fluid induced pressure forcesalong the outer diameter surface 51. The resultant force balance fixesthe piston ring 35 to the outer shaft 32 so that both rotate withoutsliding. Pressure forces along the forward and aft faces 50, 49 are asdescribed in FIG. 17 h.

The description above indicates that a great degree of flexibility isoffered in terms of the present invention. Although various embodimentshave been described in considerable detail with reference to certainpreferred versions thereof, other versions are possible. Therefore, thespirit and scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

What is claimed is:
 1. An intershaft seal system disposed between anouter shaft and an inner shaft which are concentric and separatelyrotatable comprising: (a) a forward mating ring adjacent to a highpressure region; and (b) an aft mating ring adjacent to a low pressureregion, said forward mating ring and said aft mating ring separatelydisposed about and separately rotatable from a piston ring, said forwardmating ring and said aft mating ring each having a plurality ofdivergent flow grooves thereon, each said divergent flow groove includesa pair of grooves which intersect at an apex, said piston ring includesa plurality of substantially vertical channels, each said substantiallyvertical channel directly communicates at one end with an outer diametersurface of said piston ring and directly communicates at another endwith a substantially horizontal channel, each said substantiallyhorizontal channel is communicable with one said apex along said forwardmating ring and one said apex along said aft mating ring, said outerdiameter surface includes at least one outer groove directly contactinga dam, a fluid from said high pressure region directed through each saidsubstantially vertical channel into said substantially horizontalchannel and then onto said apexes as said piston ring rotates withrespect to said divergent flow grooves, each said apex directs saidfluid into said pair of grooves, said divergent flow grooves produce asubstantially symmetric fluid pressure along a forward face and an aftface of said piston ring so as to minimize twist along said piston ring.2. The intershaft seal system of claim 1, wherein said substantiallyvertical channels extend from said outer diameter surface inward towardsaid inner shaft.
 3. The intershaft seal system of claim 1, wherein adepth varies along at least one said divergent flow groove.
 4. Theintershaft seal system of claim 1, wherein a width varies along at leastone said divergent flow groove.
 5. The intershaft seal system of claim1, wherein each end of said substantially horizontal channel directlycommunicates with a groove, one said groove disposed along said aftface, one said groove disposed along said forward face, each said groovecommunicable with at least one said apex.
 6. The intershaft seal systemof claim 1, wherein said aft mating ring includes a plurality of holeswhich allow said fluid to enter said low pressure region.
 7. Theintershaft seal system of claim 1, wherein said dam prevents flow ofsaid fluid between said piston ring and said outer shaft.
 8. Theintershaft seal system of claim 1, wherein said outer groove directlycommunicates with said substantially vertical channel.
 9. An intershaftseal system disposed between an outer shaft and an inner shaft which areconcentric and separately rotatable comprising: (a) a forward matingring adjacent to a high pressure region; and (b) an aft mating ringadjacent to a low pressure region, said forward mating ring and said aftmating ring separately disposed about and separately rotatable from apiston ring, said forward mating ring and said aft mating ring eachhaving a plurality of divergent flow grooves thereon, each saiddivergent flow groove includes a pair of grooves which intersect at anapex, said piston ring includes a plurality of substantially verticalchannels, each said substantially vertical channel directly communicatesat one end with an inner diameter surface along said piston ring anddirectly communicates at another end with a substantially horizontalchannel, each said substantially horizontal channel communicable withone said apex along said forward mating ring and one said apex alongsaid aft mating ring, said forward mating ring includes at least oneport which communicates a fluid to said inner diameter surface, saidfluid from said high pressure region directed through each saidsubstantially vertical channel into said substantially horizontalchannel and then onto said apexes as said piston ring rotates withrespect to said divergent flow grooves, said apex directs said fluidinto said pair of grooves, said divergent flow grooves produce asubstantially symmetric fluid pressure along a forward face and an aftface of said piston ring so as to minimize twist along said piston ring.10. The intershaft seal system of claim 9, wherein said substantiallyvertical channels extend from said inner diameter surface outward towardsaid outer shaft.
 11. The intershaft seal system of claim 9, wherein adepth varies along at least one said divergent flow groove.
 12. Theintershaft seal system of claim 9, wherein a width varies along at leastone said divergent flow groove.
 13. The intershaft seal system of claim9, wherein each end of said substantially horizontal channel directlycommunicates with a groove, one said groove disposed along said aftface, one said groove disposed along said forward face, each said groovecommunicable with at least one said apex.
 14. The intershaft seal systemof claim 9, wherein said outer diameter surface includes at least oneouter groove directly contacting a dam, said dam prevents flow of saidfluid between said piston ring and said outer shaft.
 15. A method forminimizing twist along a piston ring disposed between an inner shaft andan outer shaft comprising the steps of: (a) communicating a fluid from ahigh pressure region to a low pressure region separated by said pistonring disposed between a forward mating ring and an aft mating ring, saidpiston ring includes a plurality of substantially vertical channels,each said substantially vertical channel directly communicates at oneend with an outer diameter surface and directly communicates at anotherend with a substantially horizontal channel; (b) directing said fluidonto a plurality of divergent flow grooves disposed along said forwardmating ring and said aft mating ring, each said divergent flow grooveincludes a pair of grooves which intersect at an apex, said fluid enterseach said substantially vertical channel and passes into saidsubstantially horizontal channel exiting onto said apexes as said pistonring rotates with respect to said divergent flow grooves, said fluidimpinges said apexes so that said fluid flows into said pairs ofgrooves, each said substantially horizontal channel communicable withone said apex along said forward mating ring and one said apex alongsaid aft mating ring; (c) producing a first fluid pressure force alongsaid forward face of said piston ring via said divergent flow grooves,said first fluid pressure force being substantially symmetric across aradial width of said piston ring; and (d) producing a second fluidpressure force along said aft face of said piston ring via saiddivergent flow grooves, said second fluid pressure force beingsubstantially symmetric across said radial width of said piston ring,said first fluid pressure force and said second fluid pressure forcebeing substantially balanced.
 16. The method of claim 15, wherein saidfluid enters said substantially vertical channel adjacent to said outerdiameter surface.
 17. The method of claim 15, wherein said fluid enterssaid low pressure region via a plurality of holes along said aft matingring.
 18. The method of claim 15, wherein said forward face and said aftface each include at least one arcuate groove communicable with at leastone said horizontal channel, each said arcuate groove communicable withat least one said apex.
 19. A method for minimizing twist along a pistonring disposed between an inner shaft and an outer shaft comprising thesteps of: (a) communicating a fluid from a high pressure region to a lowpressure region separated by said piston ring disposed between a forwardmating ring and an aft mating ring, said piston ring includes aplurality of substantially vertical channels, each said substantiallyvertical channel directly communicates at one end with an inner diametersurface along said piston ring and directly communicates at another endwith a substantially horizontal channel, said forward mating ringincludes at least one port which communicates a fluid to said innerdiameter surface; (b) directing said fluid onto a plurality of divergentflow grooves disposed along said forward mating ring and said aft matingring, each said divergent flow groove includes a pair of grooves whichintersect at an apex, said fluid enters each said substantially verticalchannel and passes into said substantially horizontal channel exitingonto said apexes as said piston ring rotates with respect to saiddivergent flow grooves, said fluid impinges said apexes so that saidfluid flows into said pairs of grooves, each said substantiallyhorizontal channel communicable with one said apex along said forwardmating ring and one said apex along said aft mating ring; (c) producinga first fluid pressure force along said forward face of said piston ringvia said divergent flow grooves, said first fluid pressure force beingsubstantially symmetric across a radial width of said piston ring; and(d) producing a second fluid pressure force along said aft face of saidpiston ring via said divergent flow grooves, said second fluid pressureforce being substantially symmetric across said radial width of saidpiston ring, said first fluid pressure force and said second fluidpressure force being substantially balanced.
 20. The method of claim 19,wherein said fluid enters said substantially vertical channel adjacentto said inner diameter surface.
 21. The method of claim 19, wherein saidfluid is communicated to said inner diameter surface via said at leastone port.
 22. The method of claim 19, wherein said forward face and saidaft face each include at least one arcuate groove communicable with atleast one said horizontal channel, each said arcuate groove communicablewith at least one said apex.